CDC says U.S. travelers can avoid wearing masks in outdoor transit

TSA Keeps Face Mask Requirement On Public Transportation Through September : Coronavirus Updates : NPR

CDC study recommends double masking to reduce Covid-19 exposure, Coronavirus

CDC orders mask mandate for planes and public transportation

Do Vaccinated People Have to Wear Masks Outside? CDC to Issue Guidance Soon - Bloomberg

Does Massachusetts have one of the strictest mask mandates in the country? - The Boston Globe

USA

CDC says many Americans can now go outside without a mask

Covid can be airborne, US CDC guidelines now say - BBC News

U.S. CDC calls for masks in areas of high COVID-19 transmission, even for fully vaccinated